This makes it possible to disengage and raise the second driven axle when unladen.
Timber trucks commonly drive empty when returning to the forest. When using a tandem drive axle, the low truck mass on the axle can result in excessive bumpiness, with maintenance and drive comfort implications. By lifting one of the axles, better road grip is achieved and fuel consumption can be reduced by up to 4 per cent when the truck is driven without a load. The lift axle tyres can be lifted 140 mm off the road surface. The new lift axle has been specifically designed for heavy duty transport when loads are carried one way and the truck is empty on its return.
With the tandem axle lift, the second driven axle can be disengaged and its wheels raised off the road when the truck is driven empty. The differential in the first driven axle is replaced with a dog clutch, allowing the second driven axle to be disengaged and raised. The driver therefore has access to both the power and capacity of two driven axles (in 6X4 configuration) and also the better manoeuvrability of a single driven axle (in a 4X2 configuration). Driving with the second driven axle raised reduces the turning circle by one metre and results in less wear on tyres and suspension systems. Also, on slippery or soft surfaces, the driver can increase pressure on the first axle by raising the second driven axle, which results in better grip and reduces the risk of getting stuck. It supplies better comfort when the truck is driven empty. In-cab noise levels are lower and steering wheel vibration is reduced with only the tyres of one drive axle being in contact with the road. The Tandem Axle Lift is available for the Volvo FM, Volvo FMX, Volvo FH and Volvo FH16. Source: http://www.volvotrucks.com/trucks/global/en-gb/newsmedia/pressreleases/Pages/pressreleases.aspx?pubId=19637